We will develop the first assay for multiplexed combinations of all 14 Bone Morphogenetic Proteins. Immunoassays are the gold standard for measuring proteins in clinical samples. However these antibody- based tests neither quantitate protein analyte variants, nor multiplex across large numbers of superfamily members. In addition, the availability of polyclonal and monoclonal antibodies is limited. We propose a novel solution to these problems, firstly by modifying a mass spectrometric immunocapture assay to use affinity capture-peptides to enrich clinically relevant protein variants. Secondly by exploitin the efficient and high- throughput production of synthetic peptides from phage display libraries as targeted capture-reagents. For proof-of-concept, we will develop a quantitative prototype assay for multiplexed combinations of all 14 Bone Morphogenetic Protein (BMP) members in human plasma. Phase II will validate multiplexed assays for the whole BMP/Transforming Growth Factor-? (TGF-?) superfamily, whose 33 members play crucial roles in development, tissue maintenance, and many diseases. TGF-? superfamily members relevant to diagnostic and therapeutic applications include Myostatin (inhibition increases muscle and bone and decreases fat), BMP-2 (overexpressed in lung carcinomas, gastric carcinomas, and gliomas), BMP-4 (elevated in chronic kidney disease and coronary artery disease), BMPs 2 and 4 (overexpressed in degenerative joint disease), TGFs-? 1, 2 and 3 (complex involvement in cancer), and BMPs 2 and 7 (approved for nonunion bone fractures and spinal fusions). These new multiplexed assays will enable reliable, specific and faster detection of single or selected combinations of members of this large and important family, for the R&D, diagnostics and therapeutics markets.